1. Field of the Invention
The present invention relates to a method and apparatus for identifying paper sheets such as bank notes by using optical characteristics to determine the authenticity of the paper sheets. In particular, this invention relates to the method and apparatus which identify paper sheets by using physical characteristics such as optical characteristics to detect a pattern printed on the paper sheets.
2. Description of the Related Art
Bank notes are a typical example of paper sheets, and authentication thereof is widespread. For example, light is radiated onto a predetermined region of the bank note while the bank note is being carried along a carrying path. The permeated light and reflected light are detected, and a signal relating to the density of a pattern printed on the bank note is extracted. The extracted signal is compared with a reference signal to determine the authenticity of the bank note.
Optical detection methods basically use a single wavelength, but cannot easily identify skillful forgeries. The density information is read at a single wavelength, and is detected by using a method which tolerates fluctuating levels of the detector and the light source, discrepancies in the printing and finish of the bank notes, and dirty bank notes. As a consequence, this method overlooks bank notes which are fairly skillfully forged and determines that they are authentic.
This problem is solved by extracting separate density information using lights of at least two wavelengths, e.g. red light and infrared light, and combining these to increase precision.
However, when two or more beams of light are used, the amount of data increases, making high-speed processing impossible. Further, the identification threshold of the individual data must be widened in order to tolerate a certain degree of variation in the genuine bank notes. This makes highly precise identification difficult to achieve.
The present invention has been achieved in order to solve the above problems. It is an object of this invention to provide an identification method and apparatus for authenticating paper sheets by statistically processing information representing characteristics of bank notes, condensing the information into a small number of characteristics which are used to determine authenticity.
In order to achieve the objects described above, the present invention provides a method for identifying a paper sheet comprising separately carrying out (a) a detecting step and (b) a processing step, which are described below, for a genuine paper sheet note and a paper sheet to be checked, creating reference data based on the detecting step and the processing step carried out for the genuine note, and determining the authenticity of the paper sheet to be checked by comparing the data detected therefrom with the reference data. (a) a detecting step of detecting a plurality of pattern signals to be checked of a plurality of physical characteristics representing a pattern which is printed on the paper sheet in a predetermined region thereof. (b) a processing step of determining mutually varying contents of the plurality of patterns to be checked; and
an identification apparatus for paper sheet, comprising a signal creating unit which creates a plurality of pattern signals to be checked for a plurality of physical characteristics representing a pattern which is printed on the paper sheet in a predetermined region thereof; a processing unit which determines mutually varying contents of the plurality of patterns to be checked; a reference data storing unit which stores a pattern signal to be checked, extracted by the signal creating unit from the genuine paper sheet note, as reference data; a calculating unit which compares the reference data from the reference data storing unit with variation contents based on the pattern signal to be checked which was extracted from the paper sheet to be checked, and calculates the difference therebetween; and a determining unit which determines whether the difference calculated by the calculating unit is within a tolerance range.